Communication networks are used to transfer information, such as data, voice, text or video information, among communication devices, such as packet telephones, computer terminals, multimedia workstations, and videophones, connected to the networks. A network typically comprises nodes connected to each other, and to communication devices, by various links. Within a corporate environment, telephone service has typically been provided by a private branch exchange switch. Generally, a private branch exchange switch is an on-site facility that is typically owned or leased by a company or another entity. The private branch exchange switch interconnects the telephones within the facility and provides access to the Public Switched Telephone Network (PSTN).
Information sent from a communication device to a network may be of any form, but is often formatted into fixed-length packets or cells. Packet-switching network architectures are widely used, for example, in popular local-area network (LAN) and wide area network (WAN) protocols, such as Ethernet and asynchronous transfer mode (ATM) protocols. In a packet-switched network, data transmissions are typically divided into blocks of data, called packets, for transmission through the network. For a packet to get to its proper destination, the packet must traverse through one or more network switches, routers or intermediate systems. Increasingly, such packet telephony systems are being utilized in corporate environments.
Unlike a conventional private branch exchange environment, which is based on the circuit switching concept, i.e., each phone conversation gets a dedicated circuit, the packet data network used by the packet telephony system is typically shared with other network applications, such as web browsers, electronic mail, file and print servers. This mix of voice and data applications on the same packet network might result in a degradation of the voice quality due to packet loss, delay and jitter. In order to protect voice applications, a higher priority is typically given to voice packets in various elements of the packet network infrastructure (if allowed by the network infrastructure). However, even with this increased priority, random congestion might take place in different parts of the packet network, and specifically at the wide area network access links or within the wide area network itself. When congestion takes place, the packet telephony users are, in a sense, at the mercy of the network and the various applications running on the network. There is little, if anything, that the packet telephony administrator can do to improve the voice quality when the underlying packet network is congested.
As apparent from the above-described deficiencies with conventional systems for overload control, a need exists for an improved method and apparatus for overload control in a multi-branch packet network, such as an Internet Protocol-based private branch exchange switch. A further need exists for an overload control method and apparatus that reroutes packet telephone calls using an alternate branch in a multi-branch packet network, upon detection of congestion in a primary branch.